<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8" />
		<title>demo</title>
	</head>
	<body>
		<script type="text/javascript" >
			function Demo(a){
				this.a = a
			}

			Demo.prototype.b = 2

			const d = new Demo(1)

			console.log(d.a)
			console.log(d.b)

		</script>
	</body>
</html>